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PK87062: CONNECTIONS TIMEOUT TO SYSPLEX DISTRIBUTOR WHEN USING VIPAROUTE

A fix is available

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APAR status

  • Closed as program error.

Error description

  • Sysplex distributor is configured with VIPAROUTE.  The routing
    table is using a route with a MTU of 8992 to reach the target
    systems.  If the TCSR drops to 16 or below, a alternate route is
    looked for.  The alternate route has a smaller MTU.  If packets
    of the smaller MTU size are sent to sysplex distributor, sysplex
    distributor tries to forward them with GRE headers over the
    smaller MTU route.  No ICMP fragmentation needed messages are
    generated if the packet is dropped by a switch or router at the
    interface level.  Application connections will timeout because
    the packets will never reach the target.
    .
    VERIFICATION STEPS:
    1) VIPADISTRIBUTE configured along with VIPAROUTE
    2) MTU difference between routes used for VIPAROUTE and
    alternate route to that target
    3) Netstat VDPT will show the TCSR has descresed for a port on
    the target
    4) Netstat VCRT detail will show the interface being used on the
    connection is the interface with a smaller MTU
    5) SYSTCPIP trace option XCF will show entry:
      Refresh VIPAROUTE IPv4
      but the routing table hasn't changed.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of the IBM Communications Server   *
    *                 for z/OS Version 1 Release(s) 9, 10 and 11   *
    *                 IP and Sysplex Distributor.                  *
    ****************************************************************
    * PROBLEM DESCRIPTION: Connections using Sysplex Distributor   *
    *                      and VIPAROUTE may timeout.              *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    A VIPAROUTE is used between a Sysplex Distributor and a target
    using an initial Maximum Transmission Unit (MTU). The initial
    route may become unusable and an alternate route may be
    selected. However the initial MTU will still be used to send
    packets. If the alternate route has a smaller MTU than the
    initial route, then packets may be discarded along the
    alternate route resulting in a connection timeout.
    +-------------------------------------------------------------+
    + Please check our Communications Server for OS/390 homepages +
    + for common networking tips and fixes.  The URL for these    +
    + homepages can be found in Informational APAR II11334.       +
    +-------------------------------------------------------------+
    

Problem conclusion

  • The module EZBIPOUT has been modified to use the correct
    MTU of the route.
    
    * Cross Reference between External and Internal Names
    

Temporary fix

Comments

APAR Information

  • APAR number

    PK87062

  • Reported component name

    TCP/IP V3 MVS

  • Reported component ID

    5655HAL00

  • Reported release

    1A0

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2009-05-20

  • Closed date

    2009-06-25

  • Last modified date

    2009-08-03

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

    UK47760 UK47761 UK47762

Modules/Macros

  • EZBIPOUT
    

Fix information

  • Fixed component name

    TCP/IP V3 MVS

  • Fixed component ID

    5655HAL00

Applicable component levels

  • R1A0 PSY UK47760

       UP09/07/23 P F907

  • R1B0 PSY UK47761

       UP09/07/23 P F907

  • R190 PSY UK47762

       UP09/07/23 P F907

Fix is available

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Document Information

Modified date:
03 August 2009